An administrative division, unit, entity, area or region, also referred to as a subnational entity, constituent unit, or country subdivision, is a portion of a country or other region delineated for the purpose of administration. Administrative divisions are granted a certain degree of autonomy and are usually required to manage themselves through their own local governments. Countries are divided up into these smaller units to make managing their land and the affairs of their people easier. For example, a country may be divided into provinces, which, in turn, are divided into counties, which, in turn, may be divided in whole or in part into municipalities; and so on.

Administrative divisions are conceptually separate from dependent territories, with the former being an integral part of the state and the other being only under some lesser form of control. However, the term "administrative division" can include dependent territories as well as accepted administrative divisions (for example, in geographical databases).

For clarity and convenience the standard neutral reference for the largest administrative subdivision of a country is called the "first-level administrative division" or "first administrative level". Next smaller is called "second-level administrative division" or "second administrative level".[1][2]

In many of the following terms originating from British cultural influence, areas of relatively low mean population density might bear a title of an entity one would expect to be either larger or smaller. There is no fixed rule, for "all politics is local" as is perhaps well demonstrated by their relative lack of systemic order. In the realm of self-government, any of these can and does occur along a stretch of road—which for the most part is passing through rural unsettled countryside. Since the terms are administrative political subdivisions of the local regional government their exact relationship and definitions are subject to home rule considerations, tradition, as well as statestatute law and local governmental (administrative) definition and control. In British cultural legacy, most territorial entities begin with fairly expansive counties which encompass an appreciably large area, but which may evolve over time into a number of smaller entities.

Within those entities are the large and small cities or towns, which may or may not be the county seat. Some of the world's larger cities culturally, if not officially, span several counties and those crossing state or provincial boundaries culturally are quite common as well, but are rarely incorporated within the same municipal government. Many sister cities share a water boundary which quite often serves as a border of both cities and counties. For example, Cambridge and Boston, Massachusetts appear to the casual traveler as one large city, while locally they each are quite culturally different and occupy different counties.